1. Field of the Invention
The present invention relates to a fringe field switching liquid crystal display device and, more particularly, to a fringe field switching liquid crystal display device realizing a high contrast ratio by modifying structures of a gate electrode and a pixel electrode.
2. Description of the Prior Art
A Liquid Crystal Display (hereinafter, referred to as xe2x80x9cLCDxe2x80x9d) has advantages of lightweight, thin thickness and low power consumption, thereby being advantageously applied to a terminal of several kinds of an information apparatus and a video apparatus instead of Cathode Ray Tube (hereinafter, referred to as xe2x80x9cCRTxe2x80x9d). Especially, a TFT-LCD having a thin film transistor (hereinafter, referred to as xe2x80x9cTFTxe2x80x9d) can realize a display device having both a high quality and a large area of a screen by its improved response features and the large number of pixels.
Generally, the TFT-LCD has a disadvantage of having a narrow viewing angle by employing Twisted Nematic (TN) mode. Recently, there has been provided an In Plane Switching (hereinafter, referred to as xe2x80x9cIPSxe2x80x9d) to solve disadvantages of the narrow viewing angle of the TFT-LCD.
The IPS mode of LCD has realized a wide viewing angle, however, it still has disadvantages of a low aperture ratio and a low transmittance ratio due to the fact that a counter electrode and a pixel electrode are made of an opaque metal.
To overcome these disadvantages of the low aperture ratio and the low transmittance ratio of the IPS mode of LCD, there has been provided a Fringe Field Switching (hereinafter, referred to as xe2x80x9cFFSxe2x80x9d) mode LCD.
The FFS mode of LCD has an advantage in which a counter electrode and a pixel electrode are made of a transparent metal to thereby improve the aperture ratio and the transmittance ratio.
And, the FFS mode of LCD has another advantage in which there is no light distortion due to anisotropy of the liquid crystal since a horizontal electric field and a parabolic electric field are employed therein, and in which a wide viewing angle is accomplished since the light is transmitted through the horizontally-arranged liquid crystal.
FIG. 1 is a top plan view of conventional FFS-LCD.
Referring to FIG. 1, the FFS-LCD shows a structure in which the pixel electrodes 50 are arranged in a slit mode being symmetric with respect to a common line 30. The FFS-LCD compensates a refractive rate of the liquid crystal, thereby accomplishing an ultra wide viewing angle of a high brightness resulting in a high quality of screen.
The pixel electrode 50 forms a fringe field and a counter electrode 40 arranged in a unit pixel defined by a gate line 10 and a data line 20 on a lower substrate 8 to activate the liquid crystal 70, thereby forming a predetermined image of the FFS-LCD. Although not shown, it is noted that a rubbing direction is horizontal, a polarizing axis of an upper polarizing plate (hereinafter, referred to as xe2x80x9canalyzerxe2x80x9d) is in a vertical direction and that of a lower polarizing plate (hereinafter, referred to as xe2x80x9cpolarizerxe2x80x9d) is in a horizontal direction. A black matrix 60 is additionally formed on an upper substrate to prevent light leakage.
However, the conventional FFS-LCD has several disadvantages as described in the following.
First, referring to FIG. 1, a strong electric field is formed on a region A between the gate line and the pixel electrode. For example, in L0 gray (that is, a black screen), xe2x88x928V of electric voltage is applied to the gate line and +5V of direct current electric voltage is applied to the pixel electrode.
As a result, 13V of strong direct current electric voltage is formed between the two electrodes.
FIG. 2 is an enlarged view of illustrating a region A of FIG. 1.
As shown in FIG. 2, the strong electric field (xcex31) is formed in a vertical direction, thereby twisting the liquid crystal 70 on the region A between the gate line 10 and the pixel electrode 50 at a predetermined angle with respect to polarizing axis (xcex11) (xcex21) of the polarizing plates and in a state of L0 gray (black screen).
Therefore, there has been a disadvantage in which the light leakage is caused by molecules of the liquid crystal spaced apart from the polarizing axis.
Also, there have been other disadvantages in which the aperture ratio is lowered thereby resulting in the low brightness since the black matrix 60 is extended on the upper substrate 9 in order to prevent the light leakage from being generated in the black screen, and in which, to the contrary, if the black matrix is narrowed to improve the aperture ratio, the light leakage is not completely prevented to thereby lower a contrast ratio.
And also, there has been disadvantage in which a large amount of light leakage causes the light leakage to generated in the L0 gray (black screen) when the molecules of the liquid crystal are spaced apart in the black matrix for cutting off the light, in case of a color filter having 3.5 of a low Optical Density (OD) in a scheme employing the resin black matrix.
Accordingly, an object of the present invention is to provide a Fringe Field Switching Liquid Crystal Display having a high contrast ratio thereby improving a high quality of screen, by modifying a structure of a gate line and a pixel electrode in order to correspond the rubbing direction to the direction of the electric field.
In order to achieve the above object, there is provided a FFS-LCD comprising: an upper substrate and a lower substrate; a gate line and a data line for defining a unit pixel, a plurality of protrusion parts being respectively formed on an edge region of the gate line adjacent to a pixel electrode, each of protrusion parts of the gate line being positioned in a depression part formed between the protrusion parts of the pixel electrode; a counter electrode formed in the unit pixel; a common line for applying a common signal to the counter electrode; a pixel electrode forming an electric field with the counter electrode, a plurality of protrusion parts being formed on an edge region of the pixel electrode adjacent to the gate line, each of protrusion parts being positioned in a depression part formed between the protrusion parts of the gate line; and a liquid crystal filled between the upper substrate and the lower substrate.